An electrical machine converts mechanical energy into electrical energy or electrical energy into mechanical energy. Depending on the use, the generator mode (conversion of mechanical energy into electrical energy) or the motor mode (conversion of electrical energy into mechanical energy) is referred to. In the case of electrical machines operated as a generator, a distinction is drawn between DC generators and AC generators.
In the case of DC generators, an electrical direct current is produced during rotation of a rotor shaft in an armature of the generator, and this electrical direct current is tapped off via a slip ring, which is fixed on the rotor shaft, by means of a sliding contact, such as a Carbon brush, for example. In the case of AC generators, slip rings are fitted to the end of a rotor shaft. During operation of the AC generator, current is supplied to the field winding from the outside via sliding contacts, such as carbon brushes, for example, which slide on the slip rings. In the process, the field winding produces a magnetic exciter field in the region of a stator winding surrounding it. During rotation of the rotor, an alternating current is induced in the coil windings of the stator.
In the case of electrical machines of the type mentioned at the outset, abraded material arises as a result of the abrasion of the sliding contacts, such as the carbon brushes, for example, on the slip rings, and this abraded material can result in electrical flashovers at the components installed there. The arcs produced in the process can result in severe damage to the installed components and the rotor shaft. In the case of conventional electrical machines, this abraded material is carried along in an uncontrolled manner in the area surrounding the slip rings by means of an air flow, which is produced by the rotary movement of the slip rings themselves or by fans.
Other electrical machines known in the prior art have suction rings, which completely surround the rotor shaft in annular fashion. These suction rings are arranged in the axial direction of the rotor shaft between two slip ring sections. In this case, the slip rings are split in the center into two slip ring sections, which extend around the entire rotor shaft. Since the sliding contacts are each arranged directly over the slip ring sections, the suction rings are arranged between sliding contacts in the axial direction of the rotor shaft. The suction rings are therefore located laterally offset with respect to the corresponding slip rings. This suction device known in the prior art requires considerable complexity in terms of construction and, as a result of the lateral offset of the suction rings with respect to the slip ring surface, does not allow optimum suction.